magick import of imagemagick has a crosshair. Here’s my function:

screnshot() {
    ## script to make screenshots with imagemagick's import command and display them
    ## usage: screenshot <path> <name>

    _id="$(date "+%Y-%m-%d_%H-%M-%S")"
    _dir="${1:-$XDG_CACHE_HOME}"
    _shot="$_dir"/"${2:-shot_$_id}.png"

    mkdir -p "$_dir"
    magick import "$_shot"
    printf '%s\n' "$_shot"
    magick display "$_shot"
}

And good old xfce4-screenshooter, xfce4-screenshooter -r and xfce4-screenshooter -w.

Edit: right, magick display. I personally like viewnior better but make it less dependencies.